Rapid out-of-band signal communication in optical components

ABSTRACT

An example embodiment includes an optoelectronic module. The optoelectronic module may be configured to transmit out-of-band (OOB) data as an average optical power difference between optical signals. The optoelectronic module may include a first optical source, a second optical source, and an optical power control device. The first optical source may be configured to generate a first optical signal including first channel payload data on a first optical channel. The second optical source may be configured to generate a second optical signal including second channel payload data on a second optical channel. The optical power control device may be configured to vary average optical powers of one or more of the first optical signal and the second optical signal to create an average optical power difference between the first optical signal and the second optical signal that is representative of a logical bit of the OOB data.

FIELD

The embodiments discussed herein are related to communication ofout-of-band signals in optical communication components.

BACKGROUND

Peripheral component interconnect express (PCIe) communication linksinclude short serial communication links, which may be used to connectperipheral devices to a computer or to connect servers, for example.PCIe communication links generally conform to a PCIe standard, whichestablishes a standard layout for a PCIe standard bus andcorrespondingly a PCIe connector that may be included in peripheraldevices. The PCIe standard is used throughout the computer industry andprovides interchangeability of peripheral devices as well as establishesdesign criteria used in the development of peripheral devices.

Specifically, the PCIe standard designates certain channels in a PCIestandard bus for communication of payload data and other channels in thePCIe standard bus for communication of status data. The payload data mayinclude general data used in applications and the status data mayinclude data rate negotiation, the presence or readiness of a peripheraldevice, and the like.

According to the PCIe standard, the data (payload data and/or statusdata) may be communicated on payload data channels, which may beconfigured into groups of four lanes or multiples of four lanes. Thelanes are generally constructed using copper components. However, thecopper components limit signaling speeds and limit distances over whichthe data may be communicated. Moreover, recent developments in the PCIestandard seek to increase the payload data speeds and users are seekinglonger distances for physically larger systems.

The subject matter claimed herein is not limited to embodiments thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one example technology area where some embodiments describedherein may be practiced.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below. This Summary is notintended to identify key features of the claimed subject matter, nor isit intended to be used as an aid in determining the scope of the claimedsubject matter.

An example embodiment includes an optoelectronic module. Theoptoelectronic module may be configured to transmit out-of-band (OOB)data as an average optical power difference between optical signals. Theoptoelectronic module may include a first optical source, a secondoptical source, and an optical power control device. The first opticalsource is configured to generate a first optical signal including firstchannel payload data on a first optical channel. The second opticalsource is configured to generate a second optical signal includingsecond channel payload data on a second optical channel. The opticalpower control device is configured to vary average optical powers of oneor more of the first optical signal and the second optical signal tocreate an average optical power difference between the first opticalsignal and the second optical signal that is representative of a logicalbit of the OOB data.

Another example embodiment may include an optoelectronic module. Theoptoelectronic module may be configured to OOB data as an averageoptical power difference between optical signals. The optoelectronicmodule may include a first optical receiver, a second optical receiver,and an optical power sensing system (sensing system). The first opticalreceiver may be configured to receive a first optical signal includingfirst channel payload data via a first optical channel. The secondoptical receiver may be configured to receive a second optical signalincluding second channel payload data via a second optical channel. Thesensing system may be configured to compare average optical powers ofthe first optical signal and the second optical signal. Additionally, inresponse to a detection of an optical power difference, the sensingsystem may be configured to output a logical bit representative of OOBdata.

Another example embodiment may include a method of communicating an OOBsignal between a host device and a target device. The method may includecommunicating a first optical signal on a first optical channel of adifferential pair of optical channels. The first optical signal mayinclude first optical channel payload data. The method may includecommunicating a second optical signal on a second optical channel of thedifferential pair. The second optical signal may include second opticalchannel payload data. The method may include comparing a first power ofthe first optical signal to a second power of the second optical signal.The method may include interpreting an optical power difference betweenthe first power and the second power as a logical bit representative ofOOB data.

The object and advantages of the embodiments will be realized andachieved at least by the elements, features, and combinationsparticularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 illustrates a block diagram of an example optical system (system)in which some embodiments may be implemented;

FIG. 2 illustrates an example active optical cable implementing anoptoelectronic module that may be included in the system of FIG. 1;

FIG. 3 illustrates an example differential out-of-band (OOB) channelthat may implement the optoelectronic module of FIG. 1;

FIGS. 4A and 4B illustrate example PCIe systems in which theoptoelectronic module of FIG. 1 may be implemented;

FIG. 5 illustrates a block diagram of an example multi-fiber active(MFA) cable implementing the optoelectronic module of FIG. 1;

FIG. 6 illustrates a block diagram of an example wavelength-divisionmultiplexing (WDM) cable implementing the optoelectronic module of FIG.1;

FIG. 7 is a flowchart illustrating an example method of communicating anoptical OOB signal between a host device and a target device; and

FIG. 8 is a flowchart illustrating another example method ofcommunicating an optical OOB signal between a host device and a targetdevice.

DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

Payload data signals on peripheral component interconnect express (PCIe)links may be carried by differential electrical signals on multiplechannels, which may be constructed of copper wires and copperconnectors. The multiple channels may be organized into groups of fourlanes or multiples of four lanes. Additionally, various upstream (e.g.,from a peripheral device to a computer) and downstream (e.g., from acomputer to a peripheral device) status data signals on a PCIe link maybe communicated via one or more additional copper conductors.

The copper conductors and copper wires limit the speed at which thepayload data signals and the status data signals may be communicated.Additionally, copper conductors and copper wires further limit distancesover which the payload data signals and the status data signals may becommunicated. For example, the copper conductors and copper wires maylimit the speed to below about 10 gigabits per second (GB/s) and fewerthan a few feet.

To meet demand for higher speeds and/or longer distances, fiber-opticsystems may be used for communicating payload data signals. For example,four-lane optoelectronic modules may be used in PCIe links. Theoptoelectronic modules may meet data transfer speeds of 10 GB/s and mayadditionally meet speeds exceeding 10 GB/s. For example, four-laneoptical transceivers may communicate at rates of about 100 GB/s and/orat multiple or various intermediate rates.

To communicate the status data in addition to payload data in opticalsystems may present some difficulties. In some optical systems,out-of-band (OOB) signals may be used to communicate status data alongoptical fibers. For example, a primary data signal, which may have ahigh data rate and a lower limit on its spectral bandwidth, and asecondary OOB data signal, which may have a lower data rate with aspectral bandwidth that does not interact with the primary data channel,may be carried in an optical signal. The OOB signals may includesideband signals, for example. However, some existing OOB signals may becommunicated below speeds customary in systems such as a PCIe system.For example, in some PCIe systems communication speeds have end-to-endlatencies on the order of 1 or 2 microseconds (μs) or less.Additionally, these optical systems may be implicitly AC coupled.Therefore, optical systems may not transmit a static DC state except byencoding the static DC state within a data stream which is inherently ACcoupled. The encoding of the static DC state may require considerableprocessing before becoming useful, which may preclude use of the opticalsystems in some environments.

Additionally, in some optical systems, electrical signals correspondingto incident optical power of the photodetector may be complexlyprocessed for other purposes not necessarily associated with thetransfer of data from one end to the other of the optical data link. Forexample, the incident optical power may be converted to a numericalvalue, scaled, offset, and calibrated numerically, and presented to hostequipment as a numerical value at a predetermined memory location forthe purpose of providing an indication of received optical power. Thisprocess may take tens of milliseconds (ms) or more.

Some embodiments discussed herein relate to communication of OOB signalssuch as the status signals in PCIe links and other implementations(e.g., quad small form-factor pluggable (qSFP), coaxpress (CXP), andcentum form-factor pluggable (CFP) compliant optical systems; multimodefiber-optical systems; multi-fiber-optical systems; wavelength divisionmultiplexed optical systems) via optical signals. An example embodimentmay include a multichannel optoelectronic module configured tocommunicate OOB data encoded in power variations of optical signalscommunicated on a pair of optical channels designated as a differentialpair with respect to the OOB data. Accordingly, the multichanneloptoelectronic module may include optical sources configured tocommunicate optical signals having varying average optical powers. Themultichannel optoelectronic module or another multichanneloptoelectronic module communicatively coupled to the multichanneloptoelectronic module may include optical receivers configured toreceive the optical signals on the differential pair and measure thevarying optical powers. The optical power differences between theoptical signals may be interpreted as OOB data. Multiple optical signalsmay be paired on which OOB differential signals are communicated toprovide additional and/or more complex OOB data.

The multichannel optoelectronic module may be implemented in an activeoptical cable and/or a peripheral device that substantially complieswith the PCIe standard. Additionally, the multichannel optoelectronicmodule may be implemented in optoelectronic systems that substantiallycomply with non-PCIe formats including qSFP, CXP, and CFP.

In embodiments implemented for PCIe-compliant devices and cables, theOOB data may be converted to electrical signals. The OOB data may becommunicated to copper connectors configured to receive status data on aPCIe link. Additionally or alternatively, the multichanneloptoelectronic module may be implemented in a multi-fiber-opticalsystem, a wavelength division multiplexed (WDM) optical system, oranother suitable optical system. The multichannel optoelectronic modulemay communicate OOB data upstream and downstream in the PCIe link and inother suitable optical systems.

The multichannel optoelectronic module may communicate OOB data at ratesin the megabit-per-second range, or may communicate singular DC coupledstatus signals with low latency typical of the PCIe standard.Additionally, communication of the OOB data in the power differences mayreduce processing needed to extract meaningful information therefrom.For example, in some existing OOB systems, bits may be communicatedevery 200 μs. It may take 10 bits to build a byte, which is about 2 msper byte. There may be about 128 bytes, which equates to about 256 msplus some overhead allocated for a header and/or a checksum, for example(about another 50 ms) to create a packet. In sum, about ⅓ of a secondmay be needed to propagate a bit from one end of an existing OOB link toanother. This may be too slow for implementations described herein.

The multichannel optoelectronic module, or at least some embodimentsthereof, may, accordingly, reduce or eliminate firmware or any similarsoftware processing to perform the processing detailed above. The lackof a need to extensively process the OOB data in the optoelectronicmodule may contribute to the effectiveness of the multichanneloptoelectronic module by reducing overall propagation delays andprocessing delays occurring at the multichannel optoelectronic module.Some additional embodiments are described with reference to theaccompanying drawings.

FIG. 1 illustrates a block diagram of an example optical system (system)100 in which some embodiments described herein may be implemented. Thesystem 100 may be configured to communicate payload data 130 and OOBdata between a host device 102 and a target device 104 on a pair ofdata-carrying optical signals 112A and 112B (generally, optical signal112 or optical signals 112). Specifically, in a depicted system 100, theoptical signals 112 may have varying average optical powers. The OOBdata, which may generally include binary and/or logical bits, may berepresented by differences or relative differences in the optical powersbetween the optical signals 112.

Communicating the OOB data as an OOB differential signal pair throughthe pair of optical signals 112 rather than as a single-ended OOB signalmay help to increase the reliability at which OOB data is communicatedbetween the host device 102 and the target device 104. Additionally,interpreting the OOB data from the optical power differences may enablecommunication of the OOB data using components with simple circuitry andlittle or no logical processing. Additionally, communicating the OOBdata from the optical power differences may enable transmission ofstatic direct current (DC) states.

In the system 100, the host device 102 and the target device 104 may becommunicatively coupled via one or more of optical channels 116A and116B (generally, optical channel 116 or optical channels 116). Theoptical signals 112 may be communicated along the optical channels 116.The optical channels 116 may include independent optical fibers and/oroptical links including one or more optical components (e.g., opticalamplifiers, dispersion compensation components, physical opticalconnectors, etc.). Alternatively, the optical channels 116 may eachinclude a different wavelength channel (or equivalent frequency channel)in a multiplexed optical system.

In FIG. 1, boxes 120A and 120B depict example optical signals 112communicated along corresponding optical channels 116. Specifically, inthe depicted embodiment, a first box 120A corresponds to a first opticalchannel 116A in which a first optical signal 112A is communicated and asecond box 120B corresponds to a second optical channel 116B in which asecond optical signal 112B is communicated. In each of the opticalsignals 112, the payload data 130 is represented by an oscillatingbinary signal. In FIG. 1, four of the payload data 130 are labeled, twoin the first optical signal 112A and two in the second optical signal112B. The OOB data is represented in the relative optical powerdifferences between the optical signals 112 at corresponding times. Forexample, an average optical power difference is represented in FIG. 1 bycomparing a first optical power 132A of the first optical signal 112A toa second optical power 132B of the second optical signal 112B over time.The first optical power 132A being greater than the second optical power132B during an OOB data bit period may be interpreted as one logical bitof OOB data, such as a logical one (or a logical zero). On the otherhand, the first optical power 132A being less than the second opticalpower 132B during an OOB data bit period may be interpreted as anotherlogical bit of OOB data, such as a logical zero (or a logical one).

Multichannel optoelectronic modules 150 (generally, optoelectronicmodule 150 or optoelectronic modules 150) may be included at each of thehost device 102 and the target device 104. The optoelectronic modules150 may be configured to generate, communicate, and/or interpret theoptical signals 112. Each of the optoelectronic modules 150 may includean optical power control device (control device) 106, optical sources108, optical receivers 110, and an optical power sensing system (sensingsystem) 118.

The optical sources 108 may include any number of suitable opticaltransmitters, which may each be coupled to one or more components (suchas a laser driver) to generate and communicate the optical signals 112including the OOB data and the payload data 130. Each of the opticalsources 108 may include, but is not limited to, a vertical cavitysurface-emitting laser (VCSEL), a transmit optical subassembly (TOSA), aFabry-Perot (FP) laser, a distributed feedback (DFB) laser, anexternally modulated (substantially constant power) laser, a laser withmanaged chirp (examples of which are marketed by FINISAR CORPORATION asCML and CHIRP MANAGED LASER CML), a tunable optical transmitter, densewavelength-division multiplexed (DWDM) transceivers, a light-emittingdiode (LED), and the like.

In some embodiments, the optical sources 108 may include a multiplicityof individual, nominally independent optical transmitters. The opticaltransmitters may be constructed in close proximity to one another and/orof a common material in the form of an array, for example. Additionallyor alternatively, the optical transmitters may be managed and/orcontrolled by one or more common systems (e.g., the control device 106).Accordingly, in these and other embodiments, drift, aging, and/ortemperature effects of the optical transmitters may be similar and maynot affect the optical power differences between the optical signals 112generated by the optical transmitters, although the absolute power ofthe optical transmitters may change.

In some embodiments, the optoelectronic module 150 may include a firstoptical source 108A configured to generate the first optical signal 112Aand a second optical source 108B configured to generate the secondoptical signal 112B, and one or more other optical sources 108configured to generate optical signals including other payload data 130and/or OOB data.

The optical receivers 110 may include any suitable optical receiverconfigured to receive the optical signals 112 and at least partiallyenable a comparison of the optical powers such that interpretation ofthe optical signals 112 may be performed.

The optical receivers 110 may generate electrical signals representativeof the optical signals 112. Specifically, the average optical power maybe represented by the bias current drawn by the optical receivers 110.The optical receivers 110 may then communicate the electrical signals tothe sensing system 118. Each of the optical receivers 110 may include,but is not limited to, a photodiode, a photodetector diode, an avalanchephotodiode, a receiver optical subassembly (ROSA), and a PIN photodiode.In some embodiments, a first of the optical receivers 110 may beconfigured to receive the first optical signal 112A and a second of theoptical receivers 110 may configured to receive the second opticalsignal 112B. Each of the first and the second of the optical receivers110 may communicate a signal representative of the average opticalpowers of the first and second optical signals 112A and 112B to, e.g.,the sensing system 118.

In some embodiments, the optical receivers 110 may include amultiplicity of individual, nominally independent optical receivers. Theoptical receivers 110 may be constructed in close proximity to oneanother and/or of a common material in the form of an array, forexample. Additionally or alternatively, the optical receivers 110 may bemanaged and/or controlled by one or more common systems. Accordingly, inthese and other embodiments, changes to the optical receivers 110 may besimilar and may not affect the optical power differences between theoptical signals 112 as measured by the optical receivers 110.

Additionally or alternatively, the optical receivers 110 may include orbe coupled to one or more components (not shown) that process theelectrical signals representative of the optical signals 112. Forexample, the host device 102 and/or the target device 104 may include atransimpedance amplifier (TIA). In some embodiments of the opticalreceivers 110, a photodiode may be connected directly to a TIA mountedwithin a ROSA. The TIA may be mounted in the ROSA or as near to thephotodiode as physically possible. Additionally or alternatively, thehost device 102 and/or the target device 104 may include a clock anddata recovery circuit (CDR), a received optical power sensing system,equalizers for optical dispersion compensation and/or precondition theelectrical output waveshape, or any multiples and/or combinationsthereof. The received optical power sensing system may include a currentmirror and a resistor or any other suitable power sensing system.

Communication of OOB data between the host device 102 and the targetdevice 104 may generally include varying one or more average opticalpowers of the optical signals 112 at a transmitting device (e.g., thehost device 102 or the target device 104). The optical signals 112having varying optical powers may be communicated to a receiving device(e.g., the other of the host device 102 or the target device 104). Theoptical power differences of the optical signals 112 may be interpretedat the receiving device as logical bits.

Correlations between the optical power differences and the logical bitsmay be organized in any suitable way. For example, in some embodiments,when the first optical power 132A is greater than the second opticalpower 132B, the receiving device may interpret the optical powerdifference as a logical one and when the second optical power 132B isgreater than the first optical power 132A, the receiving device mayinterpret the optical power difference as a logical zero. The inverseinterpretation of the optical power differences may alternately beimplemented in some embodiments.

The changes to the first and second optical powers 132A, 132B of theoptical signals 112 may be controlled by the control device 106. Anexample of the control device 106 may include a driver (or multipledrivers) that is communicatively coupled to at least some of the opticalsources 108. The driver may be a current driver and may increase ordecrease a current provided to the optical sources 108, which may varythe optical power of the optical signals 112.

In some embodiments, the control device 106 may include adigital-to-analog converter (DAC). The DAC may be configured to providea bias current to one or more of the optical sources 108. When theoptoelectronic module 150 is calibrated during manufacturing, one ormore numerical values may be determined for the DAC to create one ormore corresponding defined optical output powers for each of the opticalsources 108. The numerical value(s) determined for the DAC for each ofthe optical sources 108 may be stored in a non-volatile memory (notshown) and provided to the DAC during operation of the optical sources108.

Additionally, in some embodiments, the optoelectronic module 150 mayalso include photodiodes. The photodiodes may be optically coupled toeach of the optical sources 108. A laser bias (and accordingly, theoptical power) may be controlled by a servo using a response of thephotodiode compared against a target value stored in non-volatilememory. Alternatively, a bias current may not be controlled directly.Instead, a servo target value, a feedback value, or a response of thephotodiode monitoring the optical sources 108 may be altered in asimilar manner in response to the logical level of the OOB data.

Additionally or alternatively, the control device 106 may include amodulator. The modulator may be configured to modulate the optical powerof the optical signals 112. The OOB data may be modulated onto theoptical signals 112 in these embodiments. The optical receivers 110 mayaccordingly include an OOB data value decision threshold. The OOB datavalue decision threshold for each of the optical channels 116 may be setas an individually scaled sample of an average of optical powers of oneor more received optical signals 112. An advantage of using themodulator and the OOB data value decision threshold may include anability to utilize most or all of the optical channels 116 in eachdirection to communicate OOB data.

For example, in some embodiments, the one or more of the optical sources108 may include an externally modulated laser. The laser power of theexternally modulated laser may remain constant. The transmitted lightintensity may be controlled by modulators such as a Mach-Zender externalmodulator. In these and other embodiments, the OOB data may be similarlymixed with the payload data, but the external modulator is providing theaverage power differences. The external modulator is not limited to aMach-Zender external modulator, as other types of modulators may besimilarly implemented to electrically vary an attenuation they presentto optical signals passing through them. In these and other embodiments,there is a “bias” that sets a range of the attenuation (as similar toaverage laser power in directly modulated laser systems). A payload datasignal may be summed with the bias to produce the normal modulated lightoutput and the OOB data can additionally be summed with the bias tosignals representative of the OOB data.

The control device 106 may accordingly vary the optical power of bothoptical signals 112 as depicted in FIG. 1 or may vary the optical powerof one of the optical signals 112. For example, in some embodiments thefirst optical signal 112A may be held substantially constant averagepower and the control device 106 may alter the optical power of thesecond optical signal 112B. While these embodiments may be described asincluding a signal and a reference, and not a “true differentialsignal,” these embodiments are still described herein as differentialdue to the difference between the signal and the reference from whichthe OOB data is interpreted. In the depicted embodiment, two opticalchannels 116 are depicted as a differential pair with respect to the OOBdata. In some other embodiments, the first optical signal 112A may beheld to a substantially constant average optical power and one or moreother optical channels 116 may carry optical signals that vary inrelationship to the first optical signal 112A.

Additionally or alternatively, as shown in FIG. 1, the control device106 may vary the optical power of both of the optical signals 112, i.e.,increase the optical power of the first optical signal 112A and decreasethe optical power of the second optical signal 112B or vice versa.

The sensing system 118 may be configured to compare the optical signals112 to determine whether an optical power difference exists. Forexample, in some embodiments, the sensing system 118 may receiveelectrical signals representative of the optical signals 112 and comparevoltages or currents of the electrical signals. When an optical powerdifference exists, the sensing system 118 may additionally determinewhich of the optical signals 112 includes an optical power that isgreater. Specifically, the sensing system 118 may determine whether thefirst optical power 132A is greater than the second optical power 132Bor vice versa, which may be interpreted as a logical bit of the OOBdata.

The sensing system 118 may include an analog comparator, which mayinclude hysteresis. The analog comparator may include a positive inputconnected to an analog signal strength node of one of the opticalreceivers 110. The analog comparator may also include a negative inputconnected to an analog signal strength node of the second of the opticalreceivers 110. The first and the second of the optical receivers 110 maybe included in a pair of the optical receivers 110 that are considered adifferential pair with respect to the OOB data and, in some embodiments,not with respect to the payload data 130 (e.g., the first and the secondof the optical receivers 110 may alternately or additionally generateelectrical data signals representing the payload data 130 where theelectrical data signals are not processed as a differential pair). Anoutput of the analog comparator may include a logical one when theoptical power of the first of the optical receivers 110 is greater thanthe optical power of the second of the optical receivers 110. Likewise,the output of the analog comparator may include a logical zero when theoptical power of the first of the optical receivers 110 is less than theoptical power of the second of the optical receivers 110. The output ofthe analog comparator may then be electrically processed within theoptoelectronic module 150 to conform to the specific electricalsignaling levels of the receiving device and may be read by thereceiving device on a connector pin, for instance.

For example, the system 100 in FIG. 1 may be communicating OOB data fromthe target device 104 to the host device 102. In this example, thetarget device 104 may receive OOB data including a logical one, then alogical zero, and then a logical one. In this example, when the firstoptical signal 112A includes a greater optical power than the secondoptical signal 112B, the optical power difference may be interpreted asa logical one bit. Conversely, when the second optical power 132B of thesecond optical signal 112B is greater than the first optical power 132Aof the first optical signal 112A, the optical power difference may beinterpreted as a logical zero bit.

A first of the optical sources 108 of the optoelectronic module 150 atthe target device 104 may accordingly be configured to generate thefirst optical signal 112A having the first optical power 132A.Additionally, a second of the optical sources 108 of the optoelectronicmodule 150 at the target device 104 may be configured to generate thesecond optical signal 112B having the second optical power 132B. Duringa first duration of time 134A and a third duration of time 134C, thefirst optical power 132A may be held higher than the second opticalpower 132B. During a second duration of time 134B, the second opticalpower 132B may be held higher than the first optical power 132A.

Each of the durations of time 134A-134C are illustrated as equal inlength in FIG. 1 and may correspond to an OOB data bit period. Moregenerally, the durations of time 134A-134C may be of the same ordifferent lengths where the length of each of the durations of time134A-134C may be an integer multiple of the OOB data bit period.

In the host device 102, the first of the optical receivers 110 may beconfigured to receive the first optical signal 112A and the second ofthe optical receivers 110 may be configured to receive the secondoptical signal 112B. The sensing system 118 of the host device 102 mayreceive and compare electrical signals representative of the first andsecond optical powers 132A, 132B of the first and second optical signals112A and 112B. The optical power differences over time between the firstand second optical signals 112A and 112B may be interpreted as a seriesof logical bits of OOB data. Because the first optical power 132A isgreater than the second optical power 132B during the first and thirddurations of time 134A, 134C, the host device 102 may interpret alogical one bit for each of the first and third durations of time 134A,134C. In contrast, because the second optical power 132B is greater thanthe first optical power 132A during the second duration of time 134B,the host device 102 may interpret a logical zero bit for the secondduration of time 134B.

In the example above, the target device 104 communicates the opticalsignals 112 to the host device 102. However, communication of theoptical signals 112 from the host device 102 to the target device 104may be performed according to a similar process.

During the communication of the OOB data, the payload data 130 may becommunicated between the target device 104 and the host device 102. Theoptoelectronic module 150 may be configured such that the payload data130 may not interfere with the OOB data and vice versa. In someembodiments, the optoelectronic module 150 may distinguish theamplitudes of the payload data 130 from the amplitudes the optical powerdifferences representative of the OOB data such that the amplitudes ofthe payload data 130 may be large compared to the optical powerdifferences. Additionally or alternatively, the optoelectronic module150 may communicate the payload data 130 at a higher frequency than theoptical power differences representative of the OOB data.

For example, the logical level of the payload data 130 may move fromsignificantly less than an average power 136 to significantly more thanthe average power 136. Accordingly, small changes representing the OOBdata may not be significant to detection of the payload data 130 by theoptical receivers 110. The amount of the changes representing the OOBdata may depend on a particular system 100. In at least someembodiments, a change of about 10% may be implemented in someembodiments which may be detected by the optical receivers 110 but maynot interfere with accurate detection of the payload data 130.

Additionally, in some embodiments, the payload data 130 may be scrambledwith an encoding scheme that may eliminate long, continuous sequences oflogical ones or logical zero values. The absence of continuous sequencesmay limit interference between the OOB data and the payload data 130 dueto infrequency or absence of optical power at lower frequencies.Likewise, the optical receivers 110 may be designed to ignore opticalpower at lower frequencies. For example, it is common in embodiments inwhich the payload data 130 is communicated at GB/s data rates that thereis negligible energy below several megahertz (MHz).

Additionally, in some embodiments, the changes in optical powerrepresentative of the OOB data may slew from one logic state to theother (e.g., from a logical zero to a logical one) in more than about afew hundreds of nanoseconds (ns). For example, the slew from a logicalzero to a logical one or vice versa may occur every about 100-500 ns.The slew from one logic state to the other may not repeatedly cycle inless than a few hundreds of ns, thus the optical power associated withthe OOB data above a few MHz may be quite low and may not interfere withthe payload data 130.

Additionally, in some embodiments the sensing system 118 and someassociated circuitry may be configured to not respond to changes morerapid than a few hundreds of ns. Accordingly, the sensing system 118 mayignore or not be affected by the payload data 130.

Embodiments of the system 100 are not limited to the host device 102 andthe target device 104. In some systems 100 the optoelectronic modules150 may be constructed as separate transceiver modules, transmittermodules, receiver modules, or active optical cables including one ormore of a transceiver module, a transmitter module, and a receivermodule. The modules may be permanently installed with fiber cables orseparable connectors to the optical channels 116. Some optoelectronicmodules 150 or systems included in the modules may be constructed byco-mounting one or more components (e.g., 106, 108, 110, and 118) withother computing devices and ICs to achieve miniaturization.

In the system 100, communication of the OOB data may be interpretedaccording to any suitable protocol. In some embodiments, the protocolmay be configured to operate with OOB data communicated on the order of1 MHz, but with no significantly higher frequency components. Forinstance, several different data and encoding formats may be used tocommunicate the OOB data from one device (e.g., 102 and/or 104) to theother. Each pair of optical channels may be differentially modulated asdescribed herein with its own data stream of OOB data, and each datastream may use a different protocol without prearrangement with themanufacturer. Additionally or alternatively, an inter-host protocol forthe OOB data exchange may be established that presents no burden on theoptoelectronic module 150 or transmission of the payload data 130.

FIG. 2 illustrates an example active optical cable (active cable) 200implementing two of the optoelectronic modules 150 of FIG. 1. The activecable 200 may include a host end 202 and a target end 204, which may beconfigured to be selectively connected to a host device and a targetdevice such as the host device 102 and the target device 104 of FIG. 1.The active cable 200 may be further configured to communicate theoptical signals 112—including the optical signals 112A and 112B of FIG.1 and additionally including optical signals 112C and 112D—between thehost end 202 and the target end 204. The optical signals 112 mayrepresent payload data and OOB data that are communicated between thehost end 202 and the target end 204.

At each of the host end 202 and the target end 204, the active cable 200may include the optoelectronic module 150 of FIG. 1. The optoelectronicmodule 150 may generate, communicate, and interpret the optical signals112 including the OOB data and the payload data.

Between the host end 202 and the target end 204, the active cable 200may include one or more of the optical channels 116 of FIG. 1. In FIG.2, the optical channels 116 include optical channels 116A-116D. Subsetsof the optical channels 116 may be designated as differential pairs 210Aand 210B (generally, differential pair 210 or differential pairs 210)with respect to the OOB data. Accordingly, power levels of the opticalsignals 112 communicated along each of the optical channels 116 in thedifferential pairs 210 may be compared and OOB data may be interpretedtherefrom. The differential pairs 210 or a combination of thedifferential pairs 210 may be referred to as lanes in some embodiments.FIG. 2 depicts two differential pairs 210 each including two opticalchannels 116. However, in some alternative examples the active cable 200may include more than two differential pairs 210 in which two or moreoptical channels 116 may be included.

For example, the first optical signal 112A communicated in the firstoptical channel 116A in a first differential pair 210A may be comparedto the second optical signal 112B in the second optical channel 116B inthe first differential pair 210A. Thus, an optical power differencemeasured between the first optical signal 112A communicated via thefirst optical channel 116A and the second optical signal 112Bcommunicated via the second optical channel 116B may be interpreted as alogical bit of OOB data. Likewise, an optical power difference measuredin a second differential pair 210B, between a third optical signal 112Cand a fourth optical signal 112D may be interpreted as a logical bit ofOOB data.

In some embodiments, the differential pairs 210 may be related to oneanother. For example, the first differential pair 210A and the seconddifferential pair 210B may be related. Thus, a two logical bit signal(e.g., 10, 01, 00, or 11) may be communicated by the two relateddifferential pairs 210. More complex signals may be communicated betweenthe host end 202 and the target end 204 by relating more of thedifferential pairs 210. For example, a three logical bit signal (e.g.,000, 001, 011, etc.) may be communicated between the host end 202 andthe target end 204 by relating three differential pairs 210. Inembodiments in which the active cable 200 is configured to communicateoperational data such as bit rate negotiations, temperature trends, andoperational status, one or more two logical bit signals, each includingtwo related differential pairs 210, may be used.

Additionally, in this and other embodiments, the active cable 200 mayinclude a jacket 222. A sectional view of the jacket 222 is depicted inFIG. 2. The differential pairs 210 may be surrounded by the jacket 222.The jacket 222 may protect and/or provide support for the differentialpairs 210.

In some embodiments, the ends 202 and 204 of the active cable 200 mayeach include connectors 212. The connectors 212 may include copper pinsor other suitable electrical or optical connectors configured to contactone or more corresponding structures at the host device and/or at thetarget device. In embodiments including the connectors 212, electricalsignals representing payload data and/or OOB data may be communicatedwith the active cable 200 via the connectors 212. For example, whencommunicating payload data and OOB data from a target device to a hostdevice, electrical signals representing the payload data and/or the OOBdata may be communicated from the target device to the target end 204via the connectors 212. The electrical signals may be converted tooptical signals by the optoelectronic module 150 at the target end 204.Specifically, the optoelectronic module 150 may generate the first andsecond optical signals 112A and 112B that may be communicated along thefirst and second optical channels 116A and 116B. Each of the first andsecond optical signals 112A and 112B may individually represent adifferent portion, e.g., a different half, of the OOB data transmittedfrom the target end 204 to the host end 202. The first and secondoptical signals 112A and 112B in combination may also include opticalpower differences representing the OOB data. The optoelectronic module150 at the host end 202 may receive the first and second optical signals112A and 112B and may separate the payload data from the OOB data. Thepayload data may be converted to electrical signals and may becommunicated to the host device via the connectors 212 of the host end202. The optical powers of the first and second optical signals 112A and112B may be compared in the optoelectronic module 150 to determine theoptical power differences and the logical bits of OOB data that theoptical power differences represent. The optoelectronic module 150 inthe host end 202 may then communicate an electrical signalrepresentative of the logical bits of OOB data to the host device viathe connectors 212 included in the host end 202. In an analogous manner,payload data and/or OOB data may be communicated in the other direction,e.g., from the host device to the target device.

Modifications, additions, or omissions may be made to the embodiment ofFIG. 2 without departing from the scope of the present disclosure. Forinstance, although two differential pairs 210 are illustrated in FIG. 2,there may be more than two differential pairs 210 as denoted by ellipses214.

FIG. 3 illustrates an example differential OOB channel (differentialchannel) 300 that may be implemented in the active cable 200 of FIG. 2,for example. FIG. 3 depicts multiple components and/or items (e.g., 150,106, 108, 116, 118, and 110) already described with reference to FIGS. 1and 2. Some details of these components are not repeated with respect toFIG. 3. Specifically, the differential channel 300 depicts communicationof OOB data and payload data from a first optoelectronic module 150A toa second optoelectronic module 150B, both of which are examples of theoptoelectronic modules 150 illustrated in and described with respect toFIGS. 1 and 2. Between the first optoelectronic module 150A and thesecond optoelectronic module 150B the differential channel 300 includesthe differential pair 210 of the first and second optical channels 116Aand 116B. With reference to FIG. 3, a first lane includes the firstoptical source 108A (which is an example of the optical sources 108 ofFIG. 1), the first optical channel 116A, and a first optical receiver110A (which is an example of the optical receivers 110 of FIG. 1), and asecond lane includes the second optical source 108B (which is anotherexample of the optical sources 108 of FIG. 1), the second opticalchannel 116B, and a second optical receiver 110B (which is anotherexample of the optical receivers 110 of FIG. 1). A first optical signalis communicated along the first lane and a second optical signal iscommunicated along the second optical lane. A first lane payload data isextracted from the first optical signal, a second lane payload data isextracted from the second optical signal, and OOB data is extracted fromthe optical power differences between the first and second opticalsignals.

Specifically, the first and second optical sources 108A and 108B mayreceive OOB data at an OOB transmit data input 302. The OOB data mayinclude logical bits, for instance, represented in an electrical signal.A buffer 304 and an inverter 306 may modify the OOB data before the OOBdata is communicated to the control devices 106A and 106B. A first OOBmodulation 314 may be communicated to a first control device 106A and asecond OOB modulation 316 may be communicated to a second control device106B. The first OOB modulation 314 and the second OOB modulation 316 mayinclude opposite polarities.

Additionally, the optical sources 108 may receive payload data atpayload data inputs 308A, 308B (collectively payload data inputs 308).The first lane payload data is communicated to a first opticaltransmitter 326A and the second lane payload data is communicated to asecond optical transmitter 326B. The first and second control devices106A and 106B may generate average bias currents based on the biasvariations of the first or second optical transmitters 326A or 326Bcoupled thereto used to produce a desired average optical output power.The OOB modulations 314 and 316 are summed with the average bias to varythe average optical powers of optical signals generated by the opticaltransmitters 326. For example, a first bias current may hold the opticalpower of the first optical signal generated by the first opticaltransmitter 326A high while a second bias current may hold the opticalpower of the second optical signal generated by the second opticaltransmitter 326B low, and/or vice versa. The payload data represented inthe first and second optical signals is not affected by optical powerchanges imposed by changing the bias current of the first and secondoptical transmitters 326A and 326B. The OOB data may be represented bydifferences in optical power between the first and second opticalsignals.

The optical signals are communicated via the optical channels 116 to thefirst and second optical receivers 110A and 110B. The first opticalreceiver 110A receives the first optical signal generated by the firstoptical transmitter 326A, and the second optical receiver 110B receivesthe second optical signal generated by the second optical transmitter326B. The first optical receiver 110A extracts the first lane payloaddata included in the first optical signal. The first lane payload datais communicated to a first lane payload data output 310A. Likewise, thesecond optical receiver 110B extracts the second lane payload dataincluded in the second optical signal. The second lane payload data iscommunicated to a second lane payload data output 310B.

First and second current mirrors 324A and 324B communicate signalsrepresentative of the average optical powers of the first and secondoptical signals to the sensing system (depicted in FIG. 3 as acomparator) 118. The sensing system 118 outputs the OOB data at an OOBdata output 318.

In this and other differential channels, there may be differencesbetween actual received powers at the optical receivers 110 that exceedthe OOB modulation levels. Accordingly, in some embodiments, the opticalaverage received power electrical signal may be normalized to facilitatethe comparison of OOB modulation levels between the channels. Tonormalize the electrical representation of the average optical powerspresented to the sensing system 118, the values of sensing resistors330A and/or 330B may be changed. Positive voltage sources 320A and 320Bmay be connected to each of receiver diodes 328A and 328B through thedriving branch of the first and second current mirrors 324A and 324B.The output side of each of the first and second current mirrors 324A and324B may accordingly source a current in proportion to an averagecurrent generated by the receiver diodes 328A and 328B. A voltage acrossthe sensing resistors 330A and 330B develops according to Ohm's Law.Inputs to the sensing system 118 may be connected to the sensingresistors 330A and 330B. Therefore, the sensing system 118 compares thedifference between two voltages, each voltage being defined by thecurrent proportional to the respective average received power of eachlane, multiplied by the value of the sensing resistors 330A and 330B.Other embodiments may normalize the apparent average received opticalpowers by other means.

In some embodiments, the sensing resistors 330A and 330B may be altered,which alter the actual gain of the first and second current mirrors 324Aand 324B so that the various received powers are normalizedmultiplicatively. In these and other embodiments, the sensing resistors330A and 330B may include a resistive DAC device.

Additionally, in some embodiments, values of the sensing resistors 330Aand 330B may be initially determined during manufacturing and/or changedas needed. To determine the value of each of the sensing resistors 330Aand 330B, the first and second optical transmitters 326A and 326B may beoperated at normal optical power output while coupled to theirrespective optical receivers 110A and 110B. A voltage is measured thatis proportional to average received power. When the measured voltage isdifferent from a target voltage, the value of corresponding sensingresistors 330A and/or 330B is modified. For example, when the voltagemeasured in step 2 is above the target voltage, the value of the sensingresistors 330A and/or 330B is decreased. The value of the sensingresistors 330A and/or 330B is modified until the voltage measured issufficiently close to the target voltage. The resulting value of thesensing resistors 330A and/or 330B may be stored in non-volatile memoryfor later use.

As depicted in FIG. 3, the first optoelectronic module 150A includesonly the optical sources 108 and the second optoelectronic module 150Bincludes only the optical receivers 110. In some alternativeembodiments, the first optoelectronic module 150A may additionallyinclude some optical receivers 110 and/or the second optoelectronicmodule 150B may additionally include some optical sources 108, which mayenable communication of additional OOB data and/or payload data from thesecond optoelectronic module 150B to the first optoelectronic module150A. Additionally or alternatively, the first optoelectronic module150A may include more than two optical sources 108 and the secondoptoelectronic module 150B may include more than two optical receivers110. The additional optical sources 108 and/or the optical receivers 110may enable communication of additional OOB signals from the firstoptoelectronic module 150A to the second optoelectronic module 150B. Thefirst and second optoelectronic modules 150A and 150B and thedifferential pairs 210 may be included in one or more devices or ends ofan active cable as depicted in FIG. 1 and FIG. 2, respectively.

FIGS. 4A and 4B illustrate example PCIe systems 400A and 400B in whichthe first and second optoelectronic modules 150A and 150B, which areexamples of the optoelectronic module 150 of FIG. 1, may be implemented.In a first PCIe system 400A of FIG. 4A, the active cable 200 describedwith reference to FIG. 2 may be configured to communicate payloadsignals and OOB signals (collectively, data signals) between a hostdevice 406 and a computing device 404. In a second PCIe system 400B ofFIG. 4B, a peripheral device 402 may be communicatively coupled to thecomputing device 404 such that data signals may be communicatedtherebetween.

Referring to FIGS. 4A and 4B, the computing device 404 may include oneor more buses 408 that substantially comply with the PCIe standard.Accordingly, the peripheral device 402 configured to be implemented withthe computing device 404 may also substantially comply with the PCIestandard. The active cable 200 and/or the peripheral device 402 may beconfigured to communicate the payload data signals on lanes 410A-410C(hereinafter lane 410 or lanes 410) designated in the PCIe standard toreceive the payload data and OOB data on the lanes 410 designated in thePCIe standard to receive status and/or operational data. Accordingly,the active cable 200 and/or the peripheral device 402 may includeconnectors such as the connectors 212 of FIG. 2 configured tocommunicate the OOB signals along one or more of the lanes 410designated in the PCIe standard to receive status and/or operationaldata and to communicate the payload signals along one or more of thelanes 410 designated in the PCIe standard to receive payload data.

Moreover, the active cable 200 and/or the peripheral device 402 may beconfigured to communicate the OOB data in both directions. Specifically,with reference to FIG. 4A, the OOB data may be communicated from thehost device 406 to the computing device 404 and from the computingdevice 404 to the host device 406. Likewise in FIG. 4B, the OOB data maybe communicated from the peripheral device 402 to the computing device404 and from the computing device 404 to the peripheral device 402. Inboth FIGS. 4A and 4B, the OOB data may be communicated in bothdirections simultaneously. Additionally, the OOB data may becommunicated on the optical channels 116 simultaneously with the payloaddata.

For example, the lanes 410 may include sets of related lanes 410. Eachset of the related lanes 410 may be configured to communicate four lanesof payload data. In the first PCIe system 400A, for example, a set oflanes 410 may be configured to communicate four lanes of payload databetween the computing device 404 (an “upstream” device) and the hostdevice 406 (a “downstream” device) via the peripheral device 402.Likewise, in the second PCIe system 400B, the set of lanes 410 may beconfigured to communicate four lanes of payload data between thecomputing device 404 (an “upstream” device) and the peripheral device402 (a “downstream” device). Additionally, two status signals thatoriginate in the host device 406 may be communicated to the computingdevice 404 or to the peripheral device 402 (or vice versa). Accordingly,the active cable 200 in FIG. 4A or a communicative coupling 430 betweenthe peripheral device 402 and a device side bus 414 in FIG. 4B mayinclude eight optical channels 116 (one of which is labeled in FIGS. 4Aand 4B at 116). The eight optical channels 116 may be optical fibers inthis and other embodiments. A first four optical channels 420A of theeight optical channels 116 may communicate the payload data.Additionally, the first four optical channels 420A may be divided intotwo differential pairs 210 with respect to OOB data. The twodifferential pairs 210 of the first four optical channels 420A maycommunicate two logical bits of status information. Likewise, a secondfour optical channels 420B of the eight optical channels 116 maycommunicate the payload data. Additionally, the second four opticalchannels 420B may be divided into two differential pairs 210 withrespect to OOB data that may communicate two logical bits of statusinformation. The first and second optoelectronic modules 150A and 150Bmay each include four optical sources and four optical receiversconfigured to communicate the payload data and OOB data. In someembodiments, according to the PCIe standard, the bus 408 may include oneor more PRSNT# lanes 410A and 410C and one or more WAKE# lanes 410B.Generally, the PRSNT# lanes 410A and 410C and the WAKE# lane 410B areconfigured to communicate status signals between the computing device404 and the peripheral device 402, which may be further communicated tothe host device 406 in the embodiment of FIG. 4A. The active cable 200and/or the communicative coupling 430 may thus be configured tocommunicate OOB signals via the PRSNT# lanes 410A and 410C and WAKE#lane 410B.

Specifically, in the first PCIe system 400A, the target end 204 of theactive cable 200 may be configured to connect with a connector 412 ofthe peripheral device 402. The connector 412 may receive electricalsignals representative of the OOB data which may be communicated to thePRSNT# lanes 410A and 410C and the WAKE# lane 410B of the device sidebus 414. The electrical signals representative of the OOB may becommunicated to the PRSNT# lanes 410A and 410C and the WAKE# lane 410Bof the bus 408. The electrical signals may then be communicated from thebus 408 to a sub-system 418 of the computing device 404. Additionally,the sub-system 418 may generate or otherwise receive operational data.Electrical signals representing the operational data may be communicatedto the bus 408. The electrical signals may be communicated to the PRSNT#lanes 410A and 410C and the WAKE# lane 410B of the bus 408 then to thePRSNT# lanes 410A and 410C and the WAKE# lane 410B of the device sidebus 414. The electrical signals may then be communicated to the targetend 204 via the connector 412. The second optoelectronic module 150B maygenerate optical signals (e.g., optical signals 112 of FIGS. 1 and 2)including optical power differences representative of the electricalsignals. The OOB data may be communicated to the host end 202. The hostend 202 may also include the first optoelectronic module 150A thatconverts the OOB data to electrical signals representative of theoperational data generated by the sub-system 418. The electrical signalsmay be communicated to the host device 406.

Additionally, in the second PCIe system 400B, the second optoelectronicmodule 150B may be coupled to the device side bus 414. The secondoptoelectronic module 150B may receive electrical signals representativeof the OOB data from the peripheral device 402. The electrical signalsrepresentative of the OOB data may be communicated to the PRSNT# lanes410A and 410C and the WAKE# lane 410B of the device side bus 414. Theelectrical signals representative of the OOB data may be communicated tothe PRSNT# lanes 410A and 410C and the WAKE# lane 410B of the bus 408.The electrical signals may then be communicated from the bus 408 to thesub-system 418 of the computing device 404. Additionally, the sub-system418 may generate or otherwise receive operational data. Electricalsignals representing the operational data may be communicated to the bus408. The electrical signals may be communicated to the PRSNT# lanes 410Aand 410C and the WAKE# lane 410B of the bus 408 then to the PRSNT# lanes410A and 410C and the WAKE# lane 410B of the device side bus 414. Theelectrical signals may then be communicated to the second optoelectronicmodule 150B. The second optoelectronic module 150B may generate opticalsignals (e.g., optical signals 112 of FIGS. 1 and 2) including opticalpower differences representative of the electrical signals. The OOB datamay be communicated to the first optoelectronic module 150A at theperipheral device 402. The second optoelectronic module 150B may convertthe OOB data to electrical signals representative of the operationaldata generated by the sub-system 418. The electrical signals may becommunicated to the peripheral device 402.

In some embodiments, the active cable 200 may only include theoptoelectronic module (e.g., 150A or 150B) at the target end 204 or atthe host end 202. In these and other embodiments, the host device 406 orthe peripheral device 402 may include the optoelectronic module.Moreover, one or more of the ends 202 and/or 204 may be integrated withthe host device 406 and/or the peripheral device 402.

The first and second PCIe systems 400A and 400B generally depict an x1PCIe configuration. However, some other embodiments may be configured tobe coupled with a PCIe board formatted according to an x4, an x8, or anx16 configuration or any other variation of the PCIe standard.Furthermore, the PCIe standard is only an example of a bus standardaccording to which the active cable 200 and/or the peripheral device 402may be configured. For example, in the first PCIe system 400A or thesecond PCIe system 400B, the active cable 200 and/or the peripheraldevice 402 may substantially conform to another PCI standard, anotherserial computer expansion bus standard, or another standard deviceinterface. For instance, in some alternative embodiments (CXP in atleast some embodiments), the active cable 200 may include ten or twelveoptical channels 116 inbound and ten or twelve more outbound. In theseand other embodiments, one of the differential pairs 210 may beconfigured to communicate synchronous clock and data. Thus, inembodiments including multiple optical channels 116 there may be oneclock differential pair 210 and multiple OOB data differential pairs 210synchronous to the common clock signal communicated via the clockdifferential pair 210.

While the above describes implementations including eight, ten, andtwelve optical channels 116, some embodiments may include two or moreoptical channels without limitation. Furthermore, some embodiments mayinclude two or more optical channels communicating data (OOB data and/orpayload data) in a first direction and/or two or more optical channelscommunicating data in a second direction opposite the first direction. Anumber communicating data in the first direction may not necessarily beequivalent to the number communicating data in the second direction.

FIG. 5 illustrates a block diagram of an example multi-fiber active(MFA) cable 500 implementing the optoelectronic modules 150 of FIG. 1.The MFA cable 500 is similar to the active cable 200 described withreference to FIG. 2. Accordingly, the MFA cable 500 includes somecomponents (e.g., 202, 204, 210, and 212) of the active cable 200 andsome details of these components are not repeated with respect to FIG.5.

Generally, the MFA cable 500 may be configured to connect to a hostdevice and a target device such that payload data and the OOB data maybe communicated therebetween. Specifically, the MFA cable 500 may enablecommunication of the payload data and the OOB data from the host deviceto the target device and from the target device to the host device. TheMFA cable 500 may be configured to communicate the payload data and theOOB data simultaneously between the host end 202 and the target end 204via multiple optical signals carried on multiple independent fibersincluded in a multi-fiber (MF) link 502. One of the optoelectronicmodules 150 may be included at each of the ends 202 and 204, each ofwhich may be configured to generate, communicate, and receive thepayload data signals and/or the OOB signals.

In the MFA cable 500, each of the optoelectronic modules 150 may includemultiple optical sources (e.g., the optical sources 108 of FIG. 1), eachof which may be configured to generate one of the optical signals. Twoor more of the optical sources may be configured to generate opticalsignals in a differential signal pair with respect to OOB data. Theoptical powers of one or both of the optical signals may be varied torepresent OOB data.

In the MFA cable 500, each of the optical channels 116 may include oneof the optical fibers included in the MF link 502. The differential pair210, which may include the first and second optical channels 116A and116B, may be designated as a differential pair on which the OOB data arecommunicated. The differential OOB data may be transmitted on thedifferential pair 210 along with the payload data from the host end 202to the target end 204 via the MF link 502.

Optical receivers (e.g., the optical receivers 110 of FIG. 1) includedin one or both of the optoelectronic modules 150 may be configured toreceive the multiple signals communicated via the MF link 502. Two ofthe optical receivers may be configured to receive the differentialoptical signals. As discussed above, a comparator (e.g., the sensingsystem 118 of FIG. 1) may detect optical power differences between thedifferential optical signals and interpret the optical power differencesas OOB data.

FIG. 5 depicts the MFA cable 500 including one of the optoelectronicmodules 150 at each of the ends 202, 204. Additionally or alternatively,one or more of the optoelectronic modules 150 that generate the multipleoptical signals including the OOB data may instead be implemented in adevice such as a host device and/or a target device discussed above.Additionally or alternatively, the MFA cable 500 may be implemented in asystem such as the first and second PCIe systems 400A and 400B of FIGS.4A and 4B. The MFA cable 500 implemented in the first and second PCIesystems 400A and 400B of FIGS. 4A and 4B may include one or moreconnectors 212 configured to communicate the optical signals to lanes,etc. as designated in the PCIe or another standard.

FIG. 6 illustrates a block diagram of an example wavelength-divisionmultiplexing (WDM) cable 600 implementing the optoelectronic modules 150of FIG. 1. The WDM cable 600 is similar to the active cable 200described with reference to FIG. 2. Accordingly, the WDM cable 600includes some components (e.g., 202, 204, 210, and 212) of the activecable 200 and some details of these components are not repeated withrespect to FIG. 6.

Generally, the WDM cable 600 may be configured to connect to a hostdevice and a target device such that payload data and the OOB data maybe communicated therebetween. The WDM cable 600 may be furtherconfigured to communicate the payload data and the OOB datasimultaneously between the host end 202 and the target end 204 via a WDMsignal. One of the optoelectronic modules 150 may be included at each ofthe ends 202 and 204, which may be configured to generate, communicate,and receive the payload data signals and/or the OOB signals.

The WDM signal in each direction (e.g., the host end 202 to the targetend 204 and/or vice versa) may include multiple data-carrying opticalsignals having differing wavelengths that may be communicated along afiber 602. In some embodiments, the fiber 602 may include a single modefiber (SMF) 602. In some embodiments, the fiber 602 may include amultimode fiber (MMF). For example, these and other embodiments mayinclude a short wave, multimode, WDM qSFP+ that implements one or morevertical cavity surface-emitting lasers (VCSELs), which may be spaced inthe band between about 800 nanometers (nm) and 950 nm. Four channels ofdata-carrying optical signals maybe communicated on the MMF, in eachdirection (e.g., the host end 202 to the target end 204 and/or viceversa).

The multiple data-carrying optical signals are combined at atransmitting side (e.g., the host end 202 or the target end 204) using amultiplexer/demultiplexer 604 and separated at a receiving side (e.g.,the other of the host end 202 or the target end 204) via anothermultiplexer/demultiplexer 604.

The multiplexer/demultiplexer 604 in FIG. 6 is shown as a singlecomponent. However, in some embodiments, the multiplexer/demultiplexer604 may include one or more separate or substantially separatecomponents having differing structures. For instance, themultiplexer/demultiplexer 604 at a transmitting side may be referred toas a multiplexer, and the multiplexer/demultiplexer 604 at a receivingside may be referred to as a demultiplexer. Themultiplexer/demultiplexer 604 may include an individual multiplexer, anindividual demultiplexer, or a combination thereof. In some embodiments,the multiplexer may include a non-wavelength selective combiner.Additionally or alternatively, the demultiplexer may include a separatewavelength bandpass filter for each wavelength at each receiverchannel's individual detector.

In the WDM cable 600, each of the optoelectronic modules 150 may includemultiple optical sources (e.g., the optical sources 108 of FIG. 1), eachof which may be configured to generate an optical signal having aspecific wavelength. Two or more of the optical sources may beconfigured to generate optical signals for differential optical signalsincluding the OOB data. Specifically, the optical powers of one or bothof the OOB signals may be varied to represent OOB data.

The differential pair 210, which may include the first and secondoptical channels 116A and 116B, may be designated as a differential pairon which the OOB data are communicated. The differential OOB signals maybe transmitted on the differential pair 210, multiplexed with one ormore other optical signals, and communicated via the fiber 602 to theother multiplexer/demultiplexer 604.

Optical receivers (e.g., the optical receivers 110 of FIG. 1) may beconfigured to receive the optical signals separated by themultiplexer/demultiplexer 604. Two of the optical receivers may beconfigured to receive the differential OOB data. As discussed above, acomparator (e.g., the sensing system 118 of FIG. 1) may detect opticalpower differences between the differential OOB signals and interpret theoptical power differences as OOB data.

FIG. 6 depicts the WDM cable 600 including one of the optoelectronicmodules 150 at each of the ends 202, 204. However, the optoelectronicmodule 150 that generates a WDM signal including OOB data mayadditionally or alternatively be implemented in a device such as a hostdevice and/or a target device. Additionally or alternatively, the WDMcable 600 may be implemented in a system such as the first and secondPCIe systems 400A and 400B of FIGS. 4A and 4B. The WDM cable 600implemented in the first and second PCIe systems 400A and 400B of FIGS.4A and 4B may include one or more connectors 212 configured tocommunicate the OOB signals to lanes, etc. as designated in the PCIe oranother standard.

FIG. 7 is a flowchart of an example method 700 of communicating anoptical OOB signal between a host device and a target device. In someembodiments, the method 700 may be performed by the optoelectronicmodule 150 discussed herein. Although illustrated as discrete blocks,various blocks may be divided into additional blocks, combined intofewer blocks, or eliminated, depending on the desired implementation.

The method 700 may begin at block 702. At block 702 a first opticalsignal may be communicated. The first optical signal may be communicatedon a first optical channel. The first optical signal may include a firstoptical channel payload data. In some embodiments, the first opticalchannel may be included in a differential pair of optical channels. Atblock 704, a second optical signal may be communicated. The secondoptical signal may be communicated on a second optical channel. Thesecond optical signal may include a second optical channel payload data.The second optical channel may be included in the differential pair.

At block 706, a first power of the first optical signal may be comparedto a second power of the second optical signal. At block 708, an opticalpower difference between the first power and the second power may beinterpreted as a logical bit representative of OOB data. At block 710, athird optical signal may be communicated. The third optical signal maybe communicated on a third optical channel. The third optical signal mayinclude third optical channel payload data. In some embodiments, thethird optical channel may be included in a second differential pair ofoptical channels. At block 712, a fourth optical signal may becommunicated. The fourth optical signal may be communicated on a fourthoptical channel. The fourth optical signal may include fourth opticalchannel payload data. In some embodiments, the fourth optical signal maybe included of the second differential pair.

At block 714, a third power of the third optical signal may be comparedto a fourth power of the fourth optical signal. At block 716, an opticalpower difference between the third power and the fourth power may beinterpreted as a second logical bit representative of the OOB data.

In some embodiments, the first power and the second power may bevariable. In these and other embodiments, in response to the first powerbeing greater than the second power, the method 700 may includeinterpreting the optical power difference as a logical one bit.Additionally, in response to the second power being greater than thefirst power, the method 700 may include interpreting the optical powerdifference as a logical zero bit.

In some embodiments, the first optical signal includes a referencesignal that may have a substantially constant power. In these and otherembodiments, in response to the first power being greater than thesecond power, the method 700 may include interpreting the optical powerdifference as a logical one bit. Additionally, in response to the secondpower being greater than the first power, the method 700 may includeinterpreting the optical power difference as a logical zero bit.

At block 718, the logical bit representative of the OOB data may becommunicated to a system. In some embodiments, the system may include anoptical system. The optical system may be configured to substantiallycomply with one or more of a qSFP standard, a CXP standard, or a CFPstandard. In some embodiments, the system may include a serial computerexpansion bus. For example, the OOB data may be communicated to one ormore lanes on the serial computer expansion bus. In some embodiments,the serial computer expansion bus substantially may comply with the PCIebus standard. In these and other embodiments, the logical bitsinterpreted from the optical power difference between the first powerand the second power may be communicated on a PRSNT# lane. Additionally,the logical bits interpreted from the optical power difference betweenthe third power and the fourth power may be communicated on a WAKE#lane.

Additionally, in some embodiments, the first optical channel may includea first wavelength of a WDM optical signal and the second opticalchannel may include a second wavelength of the WDM optical signal.Alternatively, the first optical channel may include a first fiber of aMF link and the second optical channel may include a second fiber of theMF link.

One skilled in the art will appreciate that, for this and otherprocedures and methods disclosed herein, the functions performed in theprocesses and methods may be implemented in differing order.Furthermore, the outlined steps and operations are only provided asexamples, and some of the steps and operations may be optional, combinedinto fewer steps and operations, or expanded into additional steps andoperations without detracting from the disclosed embodiments.

FIG. 8 is a flowchart of another example method 800 of communicating anoptical OOB signal between a host device and a target device. In someembodiments, the method 800 may be performed by the optoelectronicmodule 150 discussed herein. Although illustrated as discrete blocks,various blocks may be divided into additional blocks, combined intofewer blocks, or eliminated, depending on the desired implementation.

The method 800 may begin at block 802. At block 802, a first opticalsignal may be communicated. The first optical signal may be communicatedon a first optical channel. The first optical signal may include a firstoptical channel payload data. At block 804, a second optical signal maybe communicated. The second optical signal may be communicated on asecond optical channel. The second optical signal may include a secondoptical channel payload data. At block 806, a third optical signal maybe communicated. The third optical signal may be communicated on a thirdoptical channel. The third optical signal may include third opticalchannel payload data. At block 808, a fourth optical signal may becommunicated. The fourth optical signal may be communicated on a fourthoptical channel. The fourth optical signal may include fourth opticalchannel payload data.

At block 810, one or more of the second power of the second opticalsignal, a third power of the third optical signal, and a fourth power ofthe fourth optical signal may be compared to a substantially constantpower of the first optical signal. At block 812, in response to one ormore of the second power, the third power, and the fourth power beinggreater than the substantially constant power, the optical powerdifference may be interpreted as a logical one bit. At block 814, inresponse to one or more of the second power, the third power, and thefourth power being less than the substantially constant power, theoptical power difference may be interpreted as a logical zero bit.

At block 816, the logical bit representative of the OOB data may becommunicated to a system. In some embodiments, the system may include anoptical system. The optical system may be configured to substantiallycomply with one or more of a qSFP standard, a CXP standard, or a CFPstandard. In some embodiments, the system may include a serial computerexpansion bus. For example, the OOB data may be communicated to one ormore lanes on the serial computer expansion bus. In some embodiments,the serial computer expansion bus substantially may comply with the PCIebus standard. In these and other embodiments, the logical bitsinterpreted from the optical power difference between the first powerand the second power may be communicated on a PRSNT# lane. Additionally,the logical bits interpreted from the optical power difference betweenthe third power and the fourth power may be communicated on a WAKE#lane.

Additionally, in some embodiments, the first optical channel may includea first wavelength of a WDM optical signal and the second opticalchannel may include a second wavelength of the WDM optical signal.Alternatively, the first optical channel may include a first fiber of aMF link and the second optical channel may include a second fiber of theMF link.

The embodiments described herein may include the use of aspecial-purpose or general-purpose computer including various computerhardware or software modules, as discussed in greater detail below.

Embodiments described herein may be implemented using computer-readablemedia for carrying or having computer-executable instructions or datastructures stored thereon. Such computer-readable media may be anyavailable media that may be accessed by a general-purpose orspecial-purpose computer. By way of example, and not limitation, suchcomputer-readable media may comprise non-transitory computer-readablestorage media including RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother non-transitory storage medium which may be used to carry or storedesired program code means in the form of computer-executableinstructions or data structures and which may be accessed by ageneral-purpose or special-purpose computer. Combinations of the aboveshould also be included within the scope of computer-readable media.

Computer-executable instructions comprise, for example, instructions anddata which cause a general-purpose computer, special-purpose computer,or special-purpose processing device to perform a certain function orgroup of functions. Although the subject matter has been described inlanguage specific to structural features and/or methodological acts, itis to be understood that the subject matter defined in the appendedclaims is not necessarily limited to the specific features or actsdescribed above. Rather, the specific features and acts described aboveare disclosed as example forms of implementing the claims.

As used herein, the term “module” or “component” may refer to softwareobjects or routines that execute on the computing system. The differentcomponents, modules, engines, and services described herein may beimplemented as objects or processes that execute on the computing system(e.g., as separate threads). While the system and methods describedherein are preferably implemented in software, implementations inhardware or a combination of software and hardware are also possible andcontemplated. In this description, a “computing entity” may be anycomputing system as previously defined herein, or any module orcombination of modulates running on a computing system.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the invention andthe concepts contributed by the inventor to furthering the art, and areto be construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present inventionshave been described in detail, it should be understood that the variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. An optoelectronic module configured to transmitout-of-band (OOB) data represented by average optical power differencesbetween two or more optical signals, the optoelectronic modulecomprising: a first optical source configured to generate a firstoptical signal including first channel payload data on a first opticalchannel; a second optical source configured to generate a second opticalsignal including second channel payload data on a second opticalchannel, the second optical channel being independent of the firstoptical channel, the first optical source includes a first laser or afirst light-emitting diode (LED), and the second optical source includesa second laser or a second LED; and an optical power control device thatincludes a modulator, wherein the optical power control device isconfigured to control an optical power of the first optical source, anoptical power of the second optical source, or optical powers of boththe first optical source and the second optical source for transmissionof a first bit of the OOB data as an OOB differential signal via thefirst optical channel and the second optical channel, the first bit ofthe OOB data being represented by an average optical power differencebetween the first optical signal and the second optical signal, and themodulator is configured to modulate the optical power of the firstoptical signal transmitted by the first laser or the first LED and theoptical power of the second optical signal transmitted by the secondlaser or the second LED.
 2. The optoelectronic module of claim 1,wherein: the first optical channel and the second optical channel are adifferential pair with respect to the OOB data; and the OOB data ismodulated on the differential pair in opposite polarities.
 3. Theoptoelectronic module of claim 1, further comprising: a third opticalsource configured to generate a third optical signal including thirdchannel payload data on a third optical channel; and a fourth opticalsource configured to generate a fourth optical signal including fourthchannel payload data on a fourth optical channel.
 4. The optoelectronicmodule of claim 3, wherein: the first and second optical channels are afirst differential pair, the third and fourth optical channels are asecond differential pair, and the optical power control device isfurther configured to control an optical power of the third opticalsource, an optical power of the fourth optical source, or optical powersof both the third optical source and the fourth optical source fortransmission of a second bit of the OOB data, the second bit of the OOBdata being represented by an average optical power difference betweenthe third optical signal and the fourth optical signal to represent thesecond bit of the OOB data.
 5. The optoelectronic module of claim 4,wherein: the first, the second, the third, and the fourth channelscorrespond to lanes on a serial computer expansion bus, the first bit ofthe OOB data is communicated on a PRSNT# lane of the serial computerexpansion bus, and the second bit of the OOB data is communicated on aWAKE# lane of the serial computer expansion bus.
 6. The optoelectronicmodule of claim 1, wherein the optical power control device isconfigured to vary current to the optical transmitters.
 7. Theoptoelectronic module of claim 6, wherein the optical power controldevice includes a bias current driver configured to vary bias current tothe optical transmitters.
 8. An active optical cable including theoptoelectronic module of claim
 1. 9. The optoelectronic module of claim1, wherein: amplitudes of the first channel payload data and the secondchannel payload data are greater than an amplitude the optical powerdifference representative of the first bit of the OOB data; frequenciesof the first channel payload data and the second channel payload dataare greater than a frequency of the optical power differencerepresentative of the first bit of the OOB data; the optical powercontrol device is configured to change the optical power of the firstoptical source and/or the optical power of the second optical sourceabout 10%; or the optical power control device is configured to controlone or more changes to the optical power of the first optical sourceand/or the optical power of the second optical source according to aslew of about 100 nanoseconds and about 500 nanoseconds.
 10. Theoptoelectronic module of claim 1, wherein the second optical channel andthe first optical channel are different wavelength channels in amultiplexed optical system.
 11. An optoelectronic module configured toreceive out-of-band (OOB) data represented by average optical powerdifferences between two or more optical signals, the optoelectronicmodule comprising: a first optical receiver configured to receive afirst optical signal including first channel payload data via a firstoptical channel; a second optical receiver configured to receive asecond optical signal including second channel payload data via a secondoptical channel, the second optical channel being independent of thefirst optical channel; a third optical receiver configured to receive athird optical signal including third channel payload data on a thirdoptical channel; a fourth optical receiver configured to receive afourth optical signal including fourth channel payload data on a fourthoptical channel; and an optical power sensing system (sensing system)configured to compare average optical powers of the first opticalsignal, the second optical signal, the third optical signal, and thefourth optical sign, wherein: the first and second optical channels area first differential pair, the third and fourth optical channels are asecond differential pair, and the sensing system is configured to detecta first optical power difference on the first differential pair and asecond differential pair, to output the first bit of the OOB data inresponse to detection of a first optical power difference on the firstdifferential pair, and to output a second bit of the OOB data inresponse to detection of an optical power difference on the seconddifferential pair.
 12. The optical module of claim 11, wherein: thefirst optical signal and the second optical signal on the firstdifferential pair include opposite polarities.
 13. The optoelectronicmodule of claim 11, wherein: the first, the second, the third, and thefourth channels correspond to one or more lanes on a serial computerexpansion bus, the first bit of the OOB data is communicated on a PRSNT#lane, and the second bit of the OOB data is communicated on a WAKE#lane.
 14. The optoelectronic module of claim 11, wherein: the firstoptical signal includes a first wavelength of a wavelength-divisionmultiplexing (WDM) signal and the second optical signal includes asecond wavelength of the WDM signal; or the first optical signal isreceived via a first fiber of a multi-fiber (MF) link and the secondoptical signal is received via a second fiber of the MF link.
 15. Anactive optical cable including the optical module of claim
 11. 16. Anoptoelectronic module configured to receive out-of-band (OOB) datarepresented by average optical power differences between two or moreoptical signals, the optoelectronic module comprising: a first opticalreceiver configured to receive a first optical signal including firstchannel payload data via a first optical channel; a second opticalreceiver configured to receive a second optical signal including secondchannel payload data via a second optical channel, the second opticalchannel being independent of the first optical channel; and an opticalpower sensing system (sensing system) configured to compare averageoptical powers of the first optical signal, the second optical signal,and in response to a detection of an optical power difference, to outputa first bit of the OOB data, wherein: the first optical receiver and thesecond optical receiver each include: a receiver diode, a sensingresistor, a positive voltage source, and a current mirror including adriving branch and an output side, the positive voltage source connectedto the receiver diode through the driving branch and the output sideconfigured to source a current in proportion to an average currentgenerated by the receiver diode such that a voltage develops on thesensing resistor; and the sensing system includes inputs from the firstoptical receiver and the second optical receiver, the inputs beingconnected to the sensing resistors of the first and second opticalreceivers.
 17. The optoelectronic module of claim 16, furthercomprising: a third optical receiver configured to receive a thirdoptical signal including third channel payload data on a third opticalchannel; and a fourth optical receiver configured to receive a fourthoptical signal including fourth channel payload data on a fourth opticalchannel; wherein: the first optical signal has a substantially constantpower, and the sensing system is configured: to output the first bit ofthe OOB data in response to detection to an optical power differencebetween the first optical signal and second optical signal; to output asecond bit of the OOB data in response to detection to an optical powerdifference between the first optical signal and the third opticalsignal; and to output a third bit of the OOB data in response todetection to an optical power difference between the first opticalsignal and the fourth optical signal.
 18. The optoelectronic module ofclaim 16, wherein a gain of the sensing system may be changed bychanging the sensing resistor, wherein the changeable gain is configuredto enable reception and comparison of signals communicated on twooptical channels having different incoming power levels.
 19. A method ofcommunicating an optical out-of-band (OOB) signal between a host deviceand a target device, the method comprising: communicating a firstoptical signal on a first optical channel, the first optical signalincluding first optical channel payload data; communicating a secondoptical signal on a second optical channel, the second optical signalincluding second optical channel payload data, the second opticalchannel being independent of the first optical channel; communicating athird optical signal on a third optical channel, the third opticalsignal including third optical channel payload data; communicating afourth optical signal on a fourth optical channel, the fourth opticalsignal including fourth optical channel payload data; comparing a firstpower of the first optical signal to a second power of the secondoptical signal; comparing a third power of the third optical signal to afourth power of the fourth optical signal; interpreting a first opticalpower difference between the first power and the second power as a firstbit of OOB data; and interpreting a second optical power differencebetween the third power and the fourth power as a second bit of the OOBdata.
 20. The method of claim 19, wherein the first power and the secondpower are variable, the method further comprising: in response to thefirst power being greater than the second power, interpreting the firstoptical power difference as a logical one bit; and in response to thesecond power being greater than the first power, interpreting the firstoptical power difference as a logical zero bit.
 21. The method of claim19, wherein the first optical signal includes a reference signal havinga substantially constant power, the method further comprising: inresponse to the first power being greater than the second power,interpreting the first optical power difference as a logical one bit;and in response to the second power being greater than the first power,interpreting the first optical power difference as a logical zero bit.22. The method of claim 19, further comprising communicating the firstbit of the OOB data to an optical system.
 23. The method of claim 19,further comprising communicating the first bit and/or the second bit ofthe OOB data to one or more lanes on a serial computer expansion bus.24. The method of claim 23, wherein: the first bit of the OOB data iscommunicated on a PRSNT# lane of serial computer expansion bus; and thesecond bit of the OOB data is communicated on a WAKE# lane of serialcomputer expansion bus.
 25. The method of claim 19, wherein: the firstoptical channel includes a first wavelength of a wavelength-divisionmultiplexing (WDM) optical signal and the second optical channelincludes a second wavelength of the WDM optical signal; or the firstoptical channel includes a first fiber of a multi-fiber (MF) link andthe second optical channel includes a second fiber of the MF link.